This application claims the priorty of International Application No. PCT/KR2004/002507, filed on Sep. 30, 2004 and Korean Application No. 2003-68283, filed Oct. 1, 2003 in the Korean Intellectual Property Office, the disclousure of which is incorporated herein in its entirety by reference.
1. Field of the Invention
The present invention relates to a structure of a package for a semiconductor image pickup device and a fabrication method thereof, and more particularly, to a structure of a package for a semiconductor image pickup device which is suitable for preventing the optical characteristics of the package for the semiconductor image pickup device from being deteriorated due to a damage of the surface of the semiconductor image pickup device in case where the package for the semiconductor image pickup device is fabricated by using flip chip bumping, and a fabrication method thereof.
2. Description of the Background Art
Generally, a semiconductor image pickup device is referred to as an image sensor chip or solid state image pickup device. They pick up the image of an object by means of a photoelectric transducer converting the image of an object into an electric signal and a charged-coupled device transmitting the electric signal converted by the photoelectric transducer and then output it as an electric signal.
In order to package the semiconductor image pickup device to a ceramic substrate, a general purpose wire bonding method is employed.
The aforementioned semiconductor image pickup device and the package of the semiconductor image pickup device employing the wire bonding method will be described in detail below with reference to the accompanying drawings.
FIG. 1 is an exemplified view showing the planar construction of a general semiconductor image pickup device. As shown therein, the semiconductor image pickup device 10 is provided at the center with an image sensing unit 20 converting the image of an object into an electrical signal and transmitting the converted electrical signal, and provided along the edges of the image sensing unit 20 with a plurality of electrode pads 30 receiving the electrical signal of the image sensing unit 20.
FIG. 2 is an exemplified view showing the sectional construction of the package for the semiconductor image pickup device employing the wire bonding method. As shown therein, the package for the semiconductor image pickup device comprises: a semiconductor image pickup device 110 attached on the middle top part of a first substrate 100 by means of a first adhesion layer 101; a second substrate 120 attached to the edges of the first substrate 100 by means of the first adhesion layer 101 so as to be spaced from the semiconductor pickup device 110 at a predetermined interval; a plurality of conductive wires 130 electrically connecting a plurality of first electrode pads 111 provided on the edges of the semiconductor image pickup device 110 and a plurality of second electrode pads 121 provided on the second substrate 120; a plurality of leads 140 extending to both sides of the top surface of the second substrate 120 from both sides of the bottom surface of the first substrate 100; supports 150 formed on the top part of the leads 140 provided on the top surface of the second substrate 120; and a glass plate 160 attached to the top part of the supports 150 by means of a second adhesion layer 102.
FIG. 3 is an exemplified view showing the module of a semiconductor image sensor in which a lens unit is coupled to the package of the semiconductor image pickup device as shown in FIG. 2. As shown therein, the package 200 for the semiconductor image pickup device as shown in FIG. 2 is provided on a module substrate 210, and a lens unit 220 is provided on the top part of the package 200 for the semiconductor image pickup device. At this time, the lens unit 220 is held by a lens holder 230 supported by the module substrate 200 and is provided on the top part of the package 200 for the semiconductor image pickup device 200.
The module size of the semiconductor image sensor as described above is entirely dependent upon the size of the package for the semiconductor image pickup device, and the package for the semiconductor image pickup device employing the wire bonding method, as shown in FIG. 2, has a problem that the package size of the semiconductor image pickup device gets bigger in comparison to the size of the semiconductor image pickup device 110, as the first electrode pads 111 of the semiconductor image pickup device 110 and the second electrode pads 121 of the second substrate 120 spaced from the semiconductor image pickup device 110 at a predetermined interval are electrically connected, thereby failing to cope with the miniaturization trend in product.
Further, there is another problem that a wire bonding process, a plastic molding process, a ceramic process, etc. are needed in order to fabricate the package for the semiconductor image pickup device by means of wire bonding, which causes a time delay and deteriorates the productivity.
To solve the above problems of the wire bonding method, a method for fabricating a package for a semiconductor image pickup device using a flip chip bumping has been recently proposed.
Generally, the method for fabricating the package for a semiconductor device using the flip chip bumping comprises: a thin film step of selectively exposing electrode pads of the semiconductor device and then depositing a metallic bonding layer and a metal layer for plating thereto; a photographic step of forming a photosensitive material selectively exposing the regions where the electrode pads of the semiconductor device are formed; a metal plating step of forming a bump on the top part of the metal layer for plating of the regions where the electrode pads are formed; an etching step of removing the photosensitive material and then removing the metal layer for plating of the regions where no bump is formed and the metallic bonding layer; and a heat treatment step of adjusting the hardness of the bump according to the purpose of use.
As described above, the respective steps of fabricating the package for the semiconductor device using the flip chip bumping are performed under the temperature condition of more than a room temperature, especially, the thin film process of depositing a metallic bonding layer and a metal layer for plating is performed under the condition of a high temperature more than 300° C.
Generally, a silicon nitride film or silicon oxide film of ceramic materials is formed on the surface of the semiconductor device to protect microcircuits formed inside the semiconductor device.
However, in case where the semiconductor device requires a specific purpose, for example, the mechanical protection, electrical property (dielectric property) enhancement, chemical protection of the semiconductor device surface or the optical characteristics thereof, inorganic matters, such as polymer, are formed on the surface of the semiconductor device. At this time, the inorganic matters, such as polymer, formed on the surface of the semiconductor device are weak in mechanical resistance and heat resistance in comparison with ceramic materials, such as the above-mentioned silicon nitride film or silicon oxide film.
Generally, the polymer formed on the surface of the semiconductor device is classified into an imide type and an epoxy type. The range of the glass transition temperature (Tg) within which the physical properties of the polymer are abruptly changed is 100 to 350° C.
Further, the tensile strength at which the polymer formed on the surface of the semiconductor device can endure without deformation is about a maximum of 400 MPa. The higher the temperature becomes, the lower the maximum tensile strength at which the polymer formed on the surface of the semiconductor device can endure without deformation becomes.
Meanwhile, a semiconductor image pickup device, which is a representative functional device the surface of which a polymer material having optical characteristics is formed on, has a polymer layer comprised of a planarization layer, a color filter layer and a micro lens stacked on the surface thereof. At this time, the color filter layer is very weak in temperature condition and thus the properties thereof are deteriorated at a high temperature more than 250° C.
Further, the polymer layer comprised of a planarization layer, a color filter layer and a micro lens stacked on the surface of the semiconductor image pickup device may be deteriorated in mechanical strength even at a temperature of 250° C. That is, in case of fabricating a package for the semiconductor image pickup device with the polymer layer stacked thereto using the aforementioned flip chip bumping method, even if the temperature condition of the thin film step of depositing a metallic bonding layer and a metal layer for plating was controlled to about 250° C. or so, the stress of a thin film generated in the deposition step exceeds the maximum tensile strength (400 MPa) at which the polymer material can endure without deformation and becomes more than 500 MPa, which leads to the deformation of the surface of the semiconductor image pickup device and thus the generation of a crack or wrinkle.
Therefore, conventionally, the semiconductor image pickup device, a representative functional device the surface of which a polymer material is formed on, has a problem that it is difficult to fabricate a package for the semiconductor image pickup device by means of flip chip bumping.